GSI

"The community GSI system is a variational data assimilation system, designed to be flexible, state-of-art, and run efficiently on various parallel computing platforms. The GSI system is in the public domain and is freely available for community use.

The Developmental Testbed Center (DTC) currently maintains and supports a community version of the GSI system (now at Version 3.5). The testing and support of this GSI system at the DTC currently focus on regional numerical weather prediction (NWP) applications coupled with the Weather Research and Forecasting (WRF) Model , but GSI can be applied to Global Forecast System(GFS) as well as other modelling systems.

GSI is an operational data assimilation system available for community use. Some of these GSI advanced features is listed as follows:

• Combined with an ensemble system, this version of GSI can be used as an 3D/4D ensemble-variational hybrid data assimilation system.
• GSI features capabilities for observation sensitivity calculation. Coupled with its global model, this feature has been used by NASA for its operational data impact study.
• The observation operators in GSI can be used in an EnKF system or other data analysis systems, transforming model variables to observed variables at the observational space.

For a complete list of the new functions and changes included in the latest release version, as well as the observation data can be used in GSI, please check these links: Version 3.5 ."

http://www.dtcenter.org/com-GSI/users/